Gas cleaners

ABSTRACT

An electrostatic filter-type gas cleaner having relatively electrically insulated discharge and collecting electrodes between which the gas to be cleaned is passed. The collecting electrodes are mounted concentrically around the discharge electrodes and are rotatable relative to them so that particles separating from the gas and depositing on the collecting electrodes are almost immediately thrown away from these electrodes. A casing surrounds the collecting electrodes and serves to collect and carry away the particles separated from the gas. The interior space of the casing is not influenced by the gas flow between the discharge and collecting electrodes.

United States Patent 11 1 Siwersson et a1.

1 51 Aug. 27, 1974 GAS CLEANERS 110.774 10/1917 Great Britain 55/154 227,450 4/1925 Great Britain.... 55/130 175] lnvemorsl one Lama" s'werswm 290.030 5/1928 Great Britain.... 55/137 Gumlar Tell, both of Helsmgborg, 319,217 2/1931 Great Britain.... 55/137 Sweden 418,551 10/1934 Great Britain..... 55/118 563,130 9/1958 Canada 55/120 [73] Assgnee' AB Mulotekmk fielsmgborg 613,018 H1961 Canada 55/122 Swede" 947,642 1/1949 France 55 149 22 Filed; July 27 1973 533,036 9/1931 Germany 55/127 258,521 4/1970 U.S.S.R 55/149 [21] Appl. No.: 383,313 v Primary ExaminerDennis E. Talbert, Jr. 1 Foreign Appllwmn Priority Data Attorney, Agent, or Firm-Karl W. Flocks Aug. 10. 1972 Sweden 10421/72 52 us. c1 55/113, 55/73, 55/120, 57 ABSTRACT 55/15413/284, 204/193 An electrostatic filter-type gas cleaner having rela- Cl. tively electrically insulated discharge and collecting Fleld of Search electrodes between the gas to be cleaned i i 117, I18, I20, 122, i 14, passed. The collecting electrodes are mounted con- 23/284, 235 centrically around the discharge electrodes and are rotatable relative to them so that particles separating 1 References Cited from the gas and depositing on the collecting elec- UNITED STATESPATENTS trodes are almost immediately thrown away from 1.329.817 2/1920 Wolcott 55 122 x Ihfise electmdes- A Casing Surrounds the collecting 1.456.044 5/1923 Strong 55/149 x electrodes and serves to collect and Carry y the 2.064.960 12/1936 Thorne 55!! 18 X particles separated from the gas. The interior space of 2.l19.297 5/1938 Scott 55/ 127 X the casing is not influenced by the gas flow between 3.443.362 5/1969 Ebert 310/2 X the discharge and collecting electrodes, 3.500.614 3/1970 Soo 55/400 X FOREIGN PATENTS OR APPLICATIONS 2 Claims, 2 Drawing Figures 116.325 2/1930 Austria 55/149 C 5 1e /a\ m GAS CLEANERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to gas cleaners and particularly to an improvement in a gas cleaning apparatus of the electric precipitator type having a plurality of discharge and collecting electrodes, said discharge electrodes being insulated from said collecting electrodes and separated therefrom to form a gap therebetween, a voltage source connected between said discharge electrodes and said collecting electrodes for establishing an electric field therebetween, and means for forcing a gas stream to be cleaned from particles suspended therein through said gap between said discharge and collecting electrodes, whereby said particles in said gas stream are attracted by said collecting electrodes for deposition thereon.

2. Description of the Prior Art Particles suspended in and to be removed from a gas are separated in an electrostatic filter by electric forces. To this end, the particles first have to be charged. The charging and the separation of the particles can take place simultaneously in a single field, or the particles can be charged in a first field and separated in a second field. The mechanism of and the manner in which the particles are charged by corona discharge are described for instance in the article Elektrofilter" by Bengt Berg, Swedish periodical Teknisk Tidskrift" 1959, PP 01-703.

The particles depositing on the collecting electrodes gradually build up a more or less well insulated particle layer on these electrodes, and an ever greater part of the voltage drop between the discharge and collecting electrodes will lie over the particle layer, while the field strength operative in the free space between the electrodes to separate the particles will become smaller and smaller. The electrostatic force attracting the charged particles thus decreases, for which reason their migration speed transversely of the direction of the gas stream and towards the collecting electrodes decreases, necessitating a longer precipitation distance with one and the same degree of separation.

Therefore, the collecting electrodes must be liberated from separated matter, which in the prior art electrostatic filters takes place intermittently or continuously in that the collecting electrodes are shaken, vibrated, mechanically scraped (dry filters), washed in, or flushed with, some suitable liquid, usually water (wet filters). These prior art procedures do not, however, provide the desirable complete cleaning of the collecting electrodes, for which reason losses occur int.al. because of the above described effects. The separation efficiency of the electrostatic filters is thus reduced compared to that of entirely clean collecting electrodes. Briefly, the losses include so-called agglomeration losses which arise in that agglomerated particles cover the collecting electrodes as a dust layer of high resistivity, so-called turbulence losses which are due to the fact that solid matter already adhering to the collecting electrodes comes loose from these at small eleccharged with a polarity opposed to that of the discharge electrodes and being repelled into the gas stream.

These losses occasion a lower migration speed of the charged particles and, as a consequence, a longer pre cipitation distance, which, to a certain extent,.may be compensated for with ensuing higher power consumption by an increase of the current density between the collecting and discharge electrodes. The current density, however, cannot to this end be increased unrestrictedly since reflective radiation occurs at a given limit and the efiiciency of separation of the filter, as a consequence, is heavily deteriorated.

SUMMARY The present invention provides an improvement of the gas cleaning apparatus outlined in the foregoing to the effect that said collecting electrodes are mounted for rotation around said discharge electrodes, means are provided for rapidly rotating aid collecting electrodes, and an outwardly closed casing connects with the outer side of said collecting electrodes, whereby said particles deposited on said collecting electrodes have kinetic energy imparted to them such that they are thrown out into said casing by centrifugal force.

As a result, the collecting electrodes can continuously be kept altogether clean from particles, which will considerably increase the separation ability of the filter compared to the previously known filters and provided the other factors that affect the separation ability remain unchanged.

Gas cleaners according to the invention thus eliminate turbulence losses, agglomeration losses and reflective radiation losses. This results in a higher migration speed of the particles, which at a constant degree of separation makes it possible to use shorter precipitation distances, i.e., smaller surfaces of the collecting electrodes and, as a consequence, smaller dimensions of the filter, or a higher flow rate of the gas through the filter, that is to say, an increase of the capacity of the filter. Moreover, the current density can be increased without any risk of reflective radiation, which provides a better efficiency of the current supplied.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a diagrammatic longitudinal section of an embodiment of the invention;

FIG. 2 illustrates a cross-section on line II-ll in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The gas cleaner illustrated in the drawings comprises a plurality of discharge electrodes 1, arranged along a cylinder surface, a plurality of collecting electrodes 2, arranged along a second cylinder surface concentrically around the discharge electrodes 1 and electrically insulated from them, an annular casing 3 enclosing the collecting electrodes 2, and a cylindrical gas inlet 4 connected onto the space between the electrodes 1 and 2 and united with the casing 3.

The discharge electrodes 1 may be thin wires, as is shown in FIG. 2, or a grid which is electrically conductive and secured between two circular, closed holders 5, 6. The lower holder 6 is fixedly mounted on a shaft 7 and is of conical configuration to conduct the gas stream, which enters from below through the inlet 4, towards a gap 8 formed between the electrodes 1 and 2. Moreover, the discharge electrodes 1 are electrically connected to a current collector 9 mounted on the shaft 7 and over which current collector there is applied a suitably negative voltage relative to that of the collecting electrodes, which are usually connected to ground.

The collecting electrodes 2 may be axially extending wires which may form part of a grid, or vanes, as shown in FIG. 2, which are electrically conductive and secured between a lower ring 10 and an upper circular holder 11 which is fixedly mounted on a shaft 14 rotatable in bearings 12. by a motor 13. The holder 11 has apertures for letting out the gas which has been highly cleaned from particles by its passage through the gap 8. The collecting electrodes 2 are furthermore electrically connected to a current collector 15 by means of which they are usually connected to ground.

The annular casing 3, enclosing the collecting electrodes 2, is sealed by sealing rings l6, 17 from the lower ring 10 and the upper holder 11 and also otherwise closed in a fully gas-tight manner to prevent the space within the casing 3 from being touched by the gas flow in the gap 8. Flushing means 18 are mounted in the upper portion of the casing 3 for flushing the axial surfaces of the casing with, e.g., water, and a gas-tight liquid drain 19 is provided at the bottom of the casing 3.

- ln operation of the filter, the gas to be cleaned from particles suspended therein is driven into the gap 8 from the inlet 4 for instance by means of an axial blower (not shown) and voltage is applied between the discharge electrodes 1 and the collecting electrodes 2, which have been set in rapid rotation by the motor 13. Passing through the gap 8, the gas is ionized because of corona discharge at the discharge electrodes 1, and the particles suspended in the gas are charged so as to be attracted by and deposit on the collecting electrodes 2. Due to the rapid rotation of the collecting electrodes 2 kinetic energy is imparted to the separated particles which are thrown by centrifugal force outwards from the collecting electrodes 2 into the space of the casing 3, where they are carried along by the flushing liquid through the drain 19. The gas cleaned from particles is discharged through the holder 11 and led off in a desired manner.

A great many modifications of the preferred embodiment described are conceivable within the scope of the invention. The embodiment described, which operates as a dry filter. can quite as well operate as a wet filter, in which case radially outwardly directed liquid sprayers are mounted in an axial row in the cylinder surface formed by the discharge electrodes l.' The liquid curtain directed from said sprayers towards the passing discharge electrodes further facilitates the removal of the particles from the collecting electrodes 2. Besides, said liquid curtain can act as a wet separator (scrubber) by facilitating agglomeration of the particles in the gas and deposition of said particles on the collecting electrodes. To this end, the gas is conducted, with the aid of the axial blower and the collecting electrodes, in a helical path through the gap 8 so that the gas flow preferably passes the liquid curtain at least twice.

The rotation of the gas flow in the gap 8 can also provide a dynamic separation (centrifugal separation) of particles. To improve this separation return channels for the gas may be provided between the lower portion of the casing 3 and the inlet 4 on the suction side of the blower, and a lower portion of the collecting electrodes may be made stationary.

In a modified embodiment the discharge electrodes can be coated externally with some dielectric, the gas being ionized without any corona discharge. The ionized field can act as a catalyst for chemical reactions of the type S0 $0 which latter is soluble in water. Alternatively, lime water can be added in the wet separator to convert $0 to CaSO which in turn can be separated and industrially exploited.

As a further alternative, the gas can be introduced into the gap 8 from the space inside the discharge electrodes which can be rotated for instance in the same direction as the collecting electrodes, the particles suspended in the gas being charged and supplied with kinetic energy at their passage through the discharge electrodes.

It should finally be mentioned that a laminar flow of the gas adjacent the collecting electrodes should be attainable by means of a suitable configuration of the collecting electrodes so that turbulence losses are further reduced.

We claim:

1. ln a gas cleaning apparatus of the electric precipitator type having a plurality of discharge and collecting electrodes, said discharge electrodes being insulated from said collecting electrodes and separated therefrom to form a gap therebetween, a voltage source connected between said discharge electrodes and said collecting electrodes for establishing an electric therebetween, and means for forcing a gas stream to be cleaned from particles suspended therein through said gap between said discharge and collecting electrodes, whereby said particles in said gas stream are attracted by said collecting electrodes for deposition thereon, the improvement wherein said discharge electrodes are mounted stationary on an inner cylinder surface, said collecting electrodes are mounted on an outer concentrical cylinder surface for rotation around said discharge electrodes, means are provided for rapidly rotating said collecting electrodes, and an outwardly closed casing connects with the outer side of said collecting electrodes, whereby said gap between said discharge and collecting electrodes is annular,'said electrical field is directed radially between said cylinder surfaces, and particles deposited on said collecting electrodes have kinetic energy imparted to them such that they are thrown out into said casing by centrifugal force.

2. A gas cleaning apparatus as claimed in claim 1, wherein flushing means are mounted in the casing for carrying away the particles separated from the gas stream. 

1. In a gas cleaning apparatus of the electric precipitator type having a plurality of discharge and collecting electrodes, said discharge electrodes being insulated from said collecting electrodes and separated therefrom to form a gap therebetween, a voltage source connected between said discharge electrodes and said collecting electrodes for establishing an electric field therebetween, and means for forcing a gas stream to be cleaned from particles suspended therein through said gap between said discharge and collecting electrodes, whereby said particles in said gas stream are attracted by said collecting electrodes for deposition thereon, the improvement wherein said discharge electrodes are mounted stationary on an inner cylinder surface, said collecting electrodes are mounted on an outer concentrical cylinder surface for rotation around said discharge electrodes, means are provided for rapidly rotating said collecting electrodes, and an outwardly closed casing connects with the outer side of said collecting electrodes, whereby said gap between said discharge and collecting electrodes is annular, said electrical field is directed radially between said cylinder surfaces, and particles deposited on said collecting electrodes have kinetic energy imparted to them such that they are thrown out into said casing by centrifugal force.
 2. A gas cleaning apparatus as claimed in claim 1, wherein flushing means are mounted in the casing for carrying away the particles separated from the gas stream. 